This chapter describes following routing features:
■ Routing
■ OSPF
■ RIP
■ Load balancing
■ DHCP server, relay agent, and client
■ DNS client and relay agent
■ Network Address Translation (NAT)
■ Mapped IP
Routing
Overview
Network devices—such as routers, switches, and workstations—are known as hosts on your LAN. The physical network is called a subnet. Hosts from different subnets communicate through routers that are connected to a WAN, as shown in Figure 29.Figure 29: LANs, WANS, and IP subnets
In the LANs above, each gateway address is the LAN IP address of the router.
When a host wants to connect to the Internet or another network outside of its LAN, it generates packets that contain the destination IP address of the remote network. The IP packets are forwarded to the LAN gateway, which looks in its routing table for the next router (hop) in the path to the remote network. The pack-ets are forwarded to that hop.
Routing tables store information about the next hop so that the router does not have to maintain the complete path to a remote host.
Routing in the router
To ensure that hosts can communicate, the Q-Series routers support the following:■ Open Shortest Path First (OSPF)
■ Routing Information Protocol (RIP)
■ Protocol-independent static routes, including a default route
■ Address Resolution Protocol (ARP)
The router supports these features for both the LAN and WAN interfaces.
To configure and manage routing protocols, use:
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The GUI Configure > Router
The CLI IP interfaces and routing commands in the CLI Reference Guide
OSPF 77
OSPF
Open Shortest Path First (OSPF) is a link-state routing protocol used by large IP networks to dynamically share information in the routing table among routers.OSPF is the more appropriate Interior Gateway Protocol (IGP) choice for larger networks, and is used more frequently than the earlier Routing Information Proto-col (RIP) because OSPF scales better.
RFC 1583 was the first widely-implemented OSPF standard, but is superseded by RFC 2328. Improvements in the OSPF standard include support for more Layer 2 network layer protocols, streamlined link state advertising, and enhanced security.
OSPF is commonly used in networks that span large geographical areas or have more than 50 routers.
To construct the link state database shared between routers, users assign a cost value for each interface. Using the cost, OSPF computes the most efficient route to each destination and selects the ideal route for network traffic passing through the router.
HELLO packets are sent periodically between routers to indicate status. Route information is exchanged between routers in Link State Advertisements (LSAs).
Using the LSAs, each router computes the shortest path to all destinations in the network and responds to network changes.
OSPF can also redistribute static routes as AS-External (ASE) routes. ASEs may be configured with their own cost and the selection of different route types may be controlled through the use of preference values.
Security for LSAs is in the form of passwords or MD5 checksums.
Setting Up OSPF
The following is an overview for setting up OSPF:1. Disable NAT on all WAN interfaces that will be running OSPF. NAT should not be used on ports connected to the Internet, as you cannot advertise private addresses to the Internet. On the Configure > Router > NAT page, clear the checkbox for NAT Enable, then select OK.
2. Allow OSPF through the firewall when using a WAN interface. If running OSPF on a WAN interface, go to Configure > System > Management Access. In the Untrusted section, select the checkbox for OSPF, then select OK.
3. Disable RIP. RIP must be disabled on the Q-Series router before OSPF can be enabled. Go to Configure > Router > RIP. Clear the Enable RIP checkbox, then select OK.
4. Enable OSPF. Go to Configure > Router > OSPF > Global Settings. Select the Enable OSPF checkbox. Enter the router ID using an IPv4 address format, such as 1.1.1.1, then select OK. This number identifies the router to other routers and must be unique.
5. Add an OSPF Area. Go to Configure > Router > OSPF. Select Add Area on the menu bar. Enter a unique area name such as Area0. Enter the unique area ID using an IPv4 address format, such as 0.0.0.0.
NOTE
Area 0.0.0.0 is a special OSPF backbone area and should be used for ports which are attached to the OSPF backbone.
6. Associate interfaces which are going to be advertised via OSPF. Go to Config-ure > Router > OSPF. From the Area section Controls list, select Associate Interfaces. Select the interfaces which will be associated with the area from the Interfaces List and select the left arrow to move them into the New Asso-ciations section, then select OK.
7. Edit the interface. Go to Configure > Router > OSPF. From the Interface sec-tion Controls list, select Edit Interface. Use the drop-down menu for Network Type and select the appropriate network type for the OSPF applica-tion. For example, an Ethernet network type would be Broadcast, a Frame Relay network type would be Point-to-Point, and a PPP network type would be Point-to-Point. Select the Enable Interface checkbox and select OK.
8. Check for discovered OSPF neighbors. Go to Configure > Router > OSPF. From the interface section, select the drop-down menu for a specific interface and select List Neighbors. This will list all of the OSPF neighbors that have been discovered or manually added. After neighbors have been discovered, the OSPF routers will exchange routing information between them. OSPF neighbors must be manually added for point-to-multipoint and NBMA (Non-Broadcast Multi Access) networks only.
9. Verify your configuration. Go to Configure > Router > Routes > Show Active Routes. This will show all active routes including those discovered by OSPF.
Limitations
OSPF load balancing is not supported in this release.NOTE
The router cannot support OSPF and RIP at the same time. RIP must be disabled before OSPF can be enabled.
To configure OSPF, use:
The GUI Configure > Router > OSPF
The CLI OSPF commands in the CLI Reference Guide
RIP 79
RIP
Routing Information Protocol (RIP) is a dynamic routing protocol used in smaller networks to exchange routing table information among less than 50 routers.Developed and popular in the 1980s, it has been replaced in large enterprises by the link-state interior routing protocol Open Shortest Path First (OSPF).
The router supports RIP versions 1 and 2 (RIP v1 and RIP v2).
RIP calculates routing tables based on the number of hops required for packets to reach their destinations. Metrics such as load, bandwidth, latency, and Maximum Transmission Units (MTUs) are not figured in the calculations. Only the cost in hops for every path to every destination is recorded.
Upon booting up, RIP routers broadcast their presence on the network using the General RIP request message, alerting neighboring RIP routers to “advertise”
their own routing tables. The original router then dynamically builds its own rout-ing table and broadcasts the information. Every 30 seconds the complete routrout-ing table is broadcast to User Datagram Protocol (UDP) port 520.
RIP does not support multipath routing, instead storing only the path with the low-est number of hops. The maximum number of hops supported is 15 — longer routes are flagged with the Internet Control Message Protocol (ICMP) message
“Destination Unreachable”.
OSPF must be disabled before RIP can be enabled and vice versa.